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• Trouble sleeping the night before the dental exam


• Feelings of nervousness that escalate while in the dental office waiting room


• Crying or feeling physically ill at the very thought of visiting the dentist


• Intense uneasiness at the thought of, or actually when, objects are placed in your mouth during the dental treatment or suddenly feeling like it is difficult to breathe

• Fear of pain. Fear of pain is a very common reason for avoiding the dentist. This fear usually stems from an early dental experience that was unpleasant or painful or from dental "pain and horror" stories told by others. Thanks to the many advances in dentistry made over the years, most of today's dental procedures are considerably less painful or even pain-free.


• Fear of injections or fear the injection won't work. Many people are terrified of needles, especially when inserted into their mouth. Beyond this fear, others fear that the anesthesia hasn't yet taken effect or wasn't a large enough dose to eliminate any pain before the dental procedure begins.

• Fear of anesthetic side effects. Some people fear the potential side effects of anesthesia such as dizziness, feeling faint, or nausea. Others don't like the numbness or "fat lip" associated with local anesthetics.

• Feelings of helplessness and loss of control. It's common for people to feel these emotions considering the situation -- sitting in a dental chair with your mouth wide open, unable to see what's going on.

• Embarrassment and loss of personal space. Many people feel uncomfortable about the physical closeness of the dentist or hygienist to their face. Others may feel self-conscious about the appearance of their teeth or possible mouth odors.

Study participants made time-to-collision judgments of images on a computer screen. The images expanded in size over one second before disappearing, to simulate "looming," an optical pattern used instinctively to judge collision time. The study participants were instructed to gauge when each of the visual stimuli on the computer screen would have collided with them by pressing a button.

The participants tended to underestimate the collision time for images of threatening objects, such as a snake or spider, as compared to non-threatening images, such as a rabbit or butterfly.

The results challenge the traditional view of looming, as a purely optical cue to object approach. "We're showing that what the object is affects how we perceive looming. If we're afraid of something, we perceive it as making contact sooner," Longo says.

"Even more striking," Lourenco adds, "it is possible to predict how much a participant will underestimate the collision time of an object by assessing the amount of fear they have for that object. The more fearful someone reported feeling of spiders, for example, the more they underestimated time-to-collision for a looming spider. That makes adaptive sense: If an object is dangerous, it's better to swerve a half-second too soon than a half-second too late."

The researchers note that it's unclear whether fear of an object makes the object appear to travel faster, or whether that fear makes the viewer expand their sense of personal space, which is generally about an arm's length away.

"We'd like to distinguish between these two possibilities in future research. Doing so will allow us to shed insight on the mechanics of basic aspects of spatial perception and the mechanisms underlying particular phobias," Lourenco says.

• choking sensation, cramp in throat;
• rapid heart;
• weakness, consternation;
• feeling of faint coming;
• abundant cold sweat;
• feeling of horror;
• shiver in the whole body;
• vomiting or diarrhea;
• feeeling that you go mad.